In the formation of integrated circuits, the components of the integrated circuits need to be patterned to form desirable shapes. A typical patterning process includes forming a photo resist, exposing the photo resist using a lithography mask, patterning the photo resist, and using the patterned photo resist to etch a layer underlying the photo resist. As a result, the layout of the patterned photo resist is transferred to the underlying layers. The photo resist is then removed.
In the patterning of photo resists, various factors, such as optical proximity effect, may cause the patterns of the photo resists to deviate from the patterns in the respective lithography masks. The deviation may be referred to as a bias. In certain locations such as at the line ends of the photo resist lines, the bias is more significant than in other places. The non-uniformity of the bias cause problems for the integrated circuit manufacturing processes.